August 26, 1920] 



NATURE 



811 



of air, a large number of experiments were per- 

 formed in which the chamber, Fig. i, was held 

 in a support, Fig. 3, and fired in a 3-in. pipe, P, 

 on a large tank. Fig. 4, exhausted to a low 

 pressure. These experiments demonstrated that 

 the presence of the air was not necessary for 

 reaction and that the recoil is produced by re- 

 action from the high-velocity gases that are 

 ejected. The operation of the jet in vacuo need 

 not appear mysterious if one thinks of the ejected 

 gases as a charge of fine shot moving with a 

 very high velocity. Obviously the chamber will 

 react, or "kick," when this charge is fired. 



KlG. 5.— Tank in which the gases struck a coil of wire-fencing. 



exactly as a shot-gun " kicks " when firing a 

 charge of ordinary shot. 



The gases were prevented from rebounding 

 from the bottom of the tank, Fig. 4, by the form 

 of the tank, the gases moving in a circular path 

 until stopped by friction. Another tank. Fig. 5, 

 was also used, in which rebound was prevented 

 by the gases striking a large coil of ^-in. mesh 

 wire-fencing. The results with both tanks 

 agreed down to the lowest pressure employed, 

 05 mm. of mercury, which is probably the 

 pressure that exists at- a height of thiirty 

 miles. 



NO. 2652, VOL. 105] 



The figures given in the Smithsonian publica- 

 tion regarding the initial masses necessary to 

 propel 1 lb. to various heights, such as 12-3 lb. 

 for 430 miles, and 438 lb. for an "infinite" 

 altitude (for the most favourable conditions, in so 

 far as they are set forth in that publication), do 

 not assume a larger velocity of ejection of the 

 gases than has been obtained experimentally, but 

 do assume a greater lightness than has so far 

 been obtained. No attempt has, however, been 

 made to reduce any part of the apparatus to the 

 minimum weight possible, and it is believed that 

 with further research such lightness as is assumed 

 is realisable. 



At the present time, the work that is being 

 done is the developing of a rocket, of small size, 

 for employing a large number of cartridges, or 

 charges, and this is being done on the remainder 

 of the original grant from the Smithsonian 

 Institution. 



Application of the Method. 



The most important of the immediate applica- 

 tions of the method is in the providing of a simple 

 and, when sufficiently developed, inexpensive 

 means of obtaining meteorological data at the 

 lo-kilometre level. It is well recognised that this 

 is the most important level for studying pressure, 

 temperature, humidity, and wind velocity ; and 

 any means of sending recording instruments 

 rapidly into this region, and of obtaining data 

 soon after the ascent has been made, is certain 

 to be of value in weather forecasting. 



At greater elevations the study of temperature, 

 pressure, wind velocity, and composition of the 

 atmosphere is of scientific importance, and also the 

 study of the aurora, during the day as well as at 

 night, and the radiations from the sun that are 

 otherwise absorbed by the atmosphere. 



A further application of much general interest 

 is the possibility of sending a mass beyond the 

 predominating gravitational field of the earth. 

 Concerning the possibility of demonstrating this 

 point by hitting the moon with a rocket, it can 

 be said, apart from the questions of aiming and 

 of correcting the flight, that the ignition of but 

 a few pounds of flash powder should be visible 

 in a powerful telescope, provided, of course, that 

 the conditions of ignition were substantially the 

 same as those in certain experiments described 

 in a recent Smithsonian publication, in which 

 1/20 of a grain fired in vacuo was observed' at a 

 distance of 2^ miles. 



Regarding these questions, as well as others 

 which naturally follow, the writer believes that 

 detailed discussion, before one has checked up 

 matters completely by experiment, is unwise, for 

 this merely precipitates a flood of useless argu- 

 ment, to which reply, in some form, must be 

 made. The ideal method, which unfortunately 

 is not always possible, is to solve a problem 

 completely, as was dome with the tests of the jet 

 in vacuo, and then to state the results. 



